Automatic gain-control system



June 8, 1937.

AUTOMATIC GAIN CONTROL SYSTEM Filed May 28, 1935 m 6%;- zm W INVENTOR ATTORNEY w. c. LANE, JR 2,083,501 7 Patented June 8, 1937 v UNITED STATES 2,083,501 AUTOMATIC GAIN-CONTROL SYSTEM William Cobb Lane,

This invention relates to gain-control systems and with particularityto an improved method and means. for automatic volume control in a sound reproducing ortsimilar signalling system.

A principal. object of the invention is to provide an'automati'cvolume control arrangement for wave transmission or reproducing systems, which arrangement possesses a rapid response to transmission level or signal level variations.

Another object is to provide an automatic volume control arrangement employing a gaincontrcl bias resistor for an amplifier tube in conjunction with a discharge tube to expedite the recovery of the gain-control.

A feature of the invention relates to the use of a condenser-resistor combination for controlling the gain of an amplifier tube, in conjunction with an electric discharge tube for expediting the discharge of the condenser to restore the system to normal gain level.

zation, arrangement and relative proportion of parts which go to make up a simple, eflicient and rapidly acting gain-control arrangement.

Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detailed description and the appended claims.

While the invention will be described herein as 0 embodied in one particular type of signalling system and employing specific kinds of apparatus, it will be understood that the invention is not necessarily limited thereto, but that this is done merely for purposes of explanation. The drawing shows in schematic diagrammatic form a typical wave repeating system embodying the invention.

Referring to the drawing, the numeral I represents schematically any well-known source of signalling current such for example as a source like. These currents are impressed through the intermediary of transformer 2 upon the rectifying device 3 preferably, although not necessarily, of the three electrode electron-emitting type. Thus as shown, device 3 comprises an evacuated envelope containing an electron-emitting cathode 4, an anode 5,'and a control-grid 6. The incoming signal waves are impressed across the cathode 4 and grid 5 preferably through the grid biasing source I, polarized as shown. The output circuit for tube 3 may be traced from the anode or plate 5, resistor 8, resistor 9, thence through the anode potential source to the cathode 55 4. Preferably a by-pass condenser llis shunted ha, Clifton, N. 1., assignor to Hygrade Sylvania. Corporation,Salem, Mass, V a corporation of Massachusetts Application May 28, 1

2 Claims. (Cl. 250-20) resistors and from the said source.

A further feature relates to the novel organiof telephone currents, telegraph currents or the PAT NT OFFICE 935, SerialNo. 23,823

around the resistors 8, 9, and source ID, to divert all but. the signalling variations from the said Preferably also, sources 1 and lllare chosen so that the tube 3 acts on that portion of its characteristic curve where it functionsasa plate circuit rectifier.

Associated with resistors 8 and 9 is another tube I2 having an electron-emitter l3, an anode or plate I4, and a discharge controlling grid H5. The tube l2 may be of the gas or vapor filled type such as a Thyratron, although preferably it is of the high vacuum type similar to tube 3. The anode-cathode discharge space of tube I2 is shunted across resistor 9, while the control-grid I9 is connected to one end of resistor 8 the opposite end of said resistor being connected to cathode l3. Preferably the resistors 8 and 9 are so proportioned that the ratio of resistance 9 to resistance 8 is approximately equal to the amplification factor of tube l2.

Also associated with resistor 9 is the amplifier tube It. While the drawing shows tube IQ of the so-called shield-grid type comprising an electron-emitter ii, a control-grid l8, a shieldrgrid l9, and an anode 29, any other well-known form of amplifier tube may be employed. The signal input circuit for tube It may be traced from the control-grid [8 through the coupling coil 2|, conductor 22, resistor 9, conductor 23, thence in parallel through the biasing resistor 24 and by-pass condenser 25 to the cathode l'l. Shunted across the resistor 9 is a condenser 26. If desired the inductance 2| may be provided with a variable tuning condenser 21 to tune the input circuit of the tube Hi to a particular frequency or group of frequencies. The shield-grid I!) may be connected to a suitable'potential tap on the direct current source 28, and likewise anode 20 may be connected through a suitable load device 29 to the source 28.

When signals of the desired level are applied to the input circuit of tube 3, there flows a predetermined magnitude of rectified current through the resistors 8 and 9. The resistors 8 and 9 and the condenser 26 are so proportioned that this normal rectified current flowing through the tube 3, charges condenser 26 to a predetermined potential which acts to control the static bias of grid l8 and consequently the level of the output from tube 16. During this normal condition of the amplifier the potential drop through resistor 8 biases the grid l5 to cut-off, that is to say, so that substantially negligible space current flows between cathode l3 and anode l4. Thus under these conditions the drop through 5 wise decreases and resistance 9 is a function-substantially.entirely of the rectified plate current of tube 3. Should the signal level on grid 6 decrease or be removed the current flow through resistor 6 likeconsequently the negative bias on grid i5 is reduced and the plate resist- ,ance of tube l2is likewise reduced. Because 01' this reduction of plate resistance 01 tube l5 and because the anode-cathode space "or tube I2 10 is in shunt to resistor 9 and also in shunt to condenser '26, the

' dinarilythe resistor-9 is of a relatively high value isand in the absence of tube '12 thedischarge oi' 1' condenser 26 is materially slowed down; However, by providing the tube l2 in parallel to the resistor 9 the discharge time of condenser 26 may be made very much lowerthus insuring rapid 20 response in the gain-control bias oi" the ampliifle'rtub'efll'tig t L i a r arious changes and modiflcations'may be ma'de' herein without departing from the spirit and scope of the invention. 5="What -,is-c1aimed is:

latter condenser discharges through the parallel combination of the resistor 9 and the anode-cathode space '01 tube i2; "Or- I sister, in

n-=a-- wave signaihngsystem, a flrst ther mimmjconn-mnafinnq '2,oss,o'o1

mionic tube upon whichincoming waves are impressed, a pair 01' resistors in the anode circuit of said tube, a second thermionic tube having its contro1-grid biasedby the potential I, drop through one of said resistors the other of said resistors being in the anode-cathode circuitfoi' said second tube, a'thirdthermionic' tube, a condenser for applying a, predetermined static bias to thegrid of said third tube, a charging circuit for said condenserincluding the second resistor, and a discharge circuit for said, condenser including the anode-cathodespace of said second tube. V. x 2. In a wave signallingisyst'em a rectifier tube upon which incoming waves are impressed, a 'g'rid controlled,discharge tube, an amplifier tube,

a pair 'of'resist'o'rs connected in series between the anodeand cathode of the rectifier tube, one of said t resistors being connected between the cathode andgrid of said secondtube, the other third ;tube, 3 and means connecting said .otherreparallel with. said ,condenser.

:oilsaid :resistors being connected ;between;the cathode and :anodeot saidsecond tube, a con-. denser for controlling-thematic grid bias oi the a 

